Step 1

Preheat the oven to 425 degrees F. Line 2 sheet pans with parchment paper.

Step 2

In a medium saute pan, cook the bacon over a medium-low heat until it begins to render, 3 to 5 minutes. Add the onions and cook until they begin to soften, about 3 minutes. Season with pepper. Set aside to let cool. Add the thyme to the cooled bacon-onion mixture.

Step 3

In a bowl, combine the farmer's cheese, creme fraiche, egg yolk and salt and pepper to taste. Set aside.

Step 4

Flour a flat surface and place the puff pastry on top. Flour the top and gently roll into a 13-by-18-inch rectangle. Cut the pastry in half and transfer each to a lined sheet pan. Using a fork, dock the puff pastry (pierce it slightly with the tines), leaving a 1-inch border untouched.

Step 5

Divide the cheese mixture between the two sheets of pastry and spread evenly on the docked area. Top each tart with half of the bacon-onion mixture.

Step 6

Place the tarts in the oven on the lower racks and bake, rotating halfway through, until the crusts are dark golden, about 25 minutes. Garnish with the pecorino and chives.